Cardiovascular disease (CVD) is a leading cause of morbidity and mortality in the United States and throughout the world. The accumulation of cholesterol in macrophages in the artery wall promotes foam-cell formation and atherosclerosis constituting a main cause of CVD (Schmitz, G. and Kaminski, W. E., “ATP-binding cassette (ABC) transporters in atherosclerosis,” Curr Atheroscler Rep., 4(3):243-51 (2002). Cholesterol accumulation in macrophages is largely dependent on the balance between the deposition by Apolipoprotein B-containing lipoprotein particles, such as VLDL, IDL and LDL, and the cholesterol removal by ApoA-I and ApoE particles. Lowering of plasma LDL concentrations by statins and other cholesterol lowering medications prevents approximately one-third of the CVD events, while two-thirds of the events remain (see, e.g., “Randomized trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S), Lancet, 344(8934):1383-1389 (1994); and “Influence of pravastatin and plasma lipids on clinical events in the West of Scotland Coronary Prevention Study (WOSCOPS), Circulation, 197(15):1440-5 (1998). The latter constitutes a huge unmet medical need.
Elevated levels of plasma HDL cholesterol are associated with reduced risk of atherosclerosis (Gordon et al., “High Density Lipoprotein As A Protective Factor Against Coronary Heart Disease,” Am. J. Med., 62:707-14 (1977)). Recent epidemiological studies have been able to ascribe the HDL protective effect to its main apolipoprotein, Apo A-I (Walldius, G, et al., High Apolipoprotein B, Low Apolipoprotein A-I, And Improvement In The Prediction of Fatal Myocardial Infarction (AMORIS study): A Prospective Study,” Lancet, 358(9298):2026-33 (2001); and Yusuf et al., “Effect of Potentially Modifiable Risk Factors Associated With Myocardial Infarction in 52 Countries (the INTERHEART study): Case-control Study,” Lancet, 364(9438):937-52 (2004)). The beneficial effects of HDL are related, in part, to activity in mediating the anti-atherogenic reverse cholesterol transport (RCT) pathway. RCT involves the transport of cholesterol from peripheral macrophages to the liver for excretion of sterol in feces (Lewis et al., “New Insights Into The Regulation of HDL Metabolism and Reverse Cholesterol Transport,” Circ. Res., 96:1221-32 (2005)). The rate-limiting step of RCT involves stimulation of cholesterol efflux from macrophages, mediated by native apolipoproteins such as Apo A-I and Apo E. This process of cholesterol efflux generates nascent HDL and requires the ATP-binding cassette transporter A1 (ABCA1) or else atherosclerosis is developed (Calpe-Berdiel et al., “Direct Evidence In Vivo of Impaired Macrophage-Specific Reverse Cholesterol Transport in ATP-Binding Cassette Transporter A1-Deficient Mice,” Biochim. Biophys. Acta., 1738 (1-3):6-9 (2005). ABCA1 is the defective molecule in Tangiers disease, which is characterized by severe deficiency in plasma HDL and premature atherosclerosis (Attie et al., “Pivotal Role of ABCA1 in Reverse Cholesterol Transport Influencing HDL Levels and Susceptibility to Atherosclerosis,” J Lipid Res., 42(11):1717-26 (2001)). Apolipoproteins A and E also stabilize cellular ABCA1 protein by preventing its degradation, which ensures high-levels of cellular cholesterol export and HDL assembly.
The clinical importance of HDL has sparked interest in the development of strategies to manipulate RCT for therapeutic purposes. Explorative proof of concept studies have shown that injections with full length Apo A-I variants, e.g., proApoA-I, Apo A-I Milano, and Apo A-I2 wild type in phospholipid complexes increases RCT (Eriksson et al., Stimulation of Fecal Steroid Excretion After Infusion of Recombinant Proapolipoprotein A-I. Potential Reverse Cholesterol Transport in Humans,” Circulation, 100(6):594-8 (1999)), and regress coronary atherosclerosis (Nissen et al., “Effect of Recombinant ApoA-I Milano on Coronary Atherosclerosis in Patients with Acute Coronary Syndromes: A Randomized Controlled Trial,” JAMA, 290(17):2292-300 (2003); and Tardif et al., “Effect of rHDL on Atherosclerosis-Safety and Efficacy (ERASE) Investigators,” JAMA, 297:1675-82. Epub March 26 (2007)). Albeit promising full length ApoA-I protein have several drawbacks as a therapeutics if they are to be developed into commercial products. For instance, Apo A-I is a 243 amino acid long protein that is far from trivial to produce in the quantities needed for a commercial product. In addition, Apo A-I variants, such as the Milano and Paris variants, may evoke immunologic responses due to their foreign nature.
Thus, there is a need in the art for additional compositions and methods utilizing the potent RCT pathway to mediate cholesterol efflux for stabilizing and regressing atherosclerotic plaques, i.e., for treating cardiovascular disease. Surprisingly, the present invention fulfills this need as well as other needs by providing such compositions and methods.